The present invention relates in general to regulating the intensity of light emitted by a lamp and more particularly concerns light dimming circuits having variable inductors.
Light dimming circuits can provide substantial energy savings by permitting a user to reduce light intensity to a desired level or by permitting automatic regulation of light intensity based on, e.g., the time of day or input from a motion detector that detects the presence of a person in a room.
Light dimming circuits for fluorescent lamps and the like are known in which light intensity is varied by adjusting the inductance of a variable inductor. Examples of such circuits are disclosed in U.S. application Ser. No. 07/484,112, filed Feb. 23, 1990, the entire disclosure of which is incorporated herein by reference. In particular, the above-mentioned U.S. application discloses a variable inductor connected in parallel with a fluorescent lamp powered by a high-frequency alternating current. Other light dimming circuits for fluorescent lamps powered at lower frequencies include a variable inductor connected in series with the lamp.
The inductance of the variable inductor disclosed in the above-mentioned U.S. application is varied by adjusting the geometry of the ferrite core around which the inductor is wrapped.